1. Field of the Invention
The present invention relates generally to an electromagnetic relay assembly and, more particularly, to the electromagnetic relay assembly of a type comprising an electromagnetic unit and at least one switch unit operatively coupled with and controlled by the electromagnetic unit.
2. Description of the Prior Art
The Japanese Laid-open Patent Publication No. 6-76717, published Mar. 18, 1994, discloses an electromagnetic relay assembly for selectively opening and closing an electric circuit including a load such as, for example, a capacitor or a lamp in which a relatively high inrush current flows when the circuit is established. This prior art electromagnetic relay assembly comprises a single casing accommodating therein an electromagnetic assembly, a movable actuator frame magnetically attracted by the electromagnetic assembly to move between first and second positions, and a switch assembly including a main switch and a sub-switch both driven by the movable actuator frame to selectively open and close an electric circuit.
Considering that the single-pole switch and the double-pole switch are generally of different sizes and require different switching mechanisms, the above mentioned prior art publication which discloses the use of the single casing for accommodating all necessary component parts that make up not only the actuator unit, but also the switch unit suggests the necessity of manufacturing two separate types of electromagnetic relay assembly; one type employing the movable actuator frame designed for exclusive use in the single-pole switch system and the other type employing the movable actuator frame designed for exclusive use in the double-pole switch system.
Thus, according to the prior art, the actuator unit cannot be commonly used with any one of the single-pole and double-pole switch systems and, consequently, manufacture of the two separate types involves an increase in cost of the resultant products. Moreover, since the double-pole type is rather complicated in structure, assemblage thereof is time-consuming.
Also, considering that the driving point of a driving piece or card used to selectively engaging and disengaging contacts together and from each other, respectively, differs in position depending on whether the switch is a single-pole switch or whether the switch is a double-pole switch, and therefore, the contacts in the single-pole switch and the contacts in the double-pole switch are driven at different speeds, there may arise problem associated with the difference in contact bounce time and driving time.
Also, in the prior art electromagnetic relay assembly, since the main switch and the sub-switch are accommodated in the same space within the single casing, carbon particles produced as a result of repeated switching of the main switch may be deposited, accompanied by reduction in contact reliability. Change of use of the sub-switch requires change of the casing and the movable actuator frame. In addition, since the yoke of the electromagnetic assembly is fixed on the bottom wall of the casing, the electromagnetic assembly tends to be often installed in an inclined fashion, resulting in failure to operate properly and deterioration in characteristic.
Moreover, in the prior art electromagnetic relay assembly, the relationship between the displacement of the movable actuator frame and the displacement of the switch contact Is determined by the ratio of leverage between the axis about which the movable actuator frame displaces and the center of the electromagnetic assembly and the position at which the driving piece or card is driven, there is no freedom of design choice of the main and auxiliary switches of the switch assembly.
Furthermore, in the prior art electromagnetic relay assembly, the electromagnetic assembly including the yoke and the coil bobbin is fixed in position inside the casing by the use of a heat-curable bonding material. Accordingly, depending on the temperature of heat used to cure the bonding material, change in characteristic tends to occur considerably and, also, during the bonding process, the damper used to provide a cushioning effect to the movement of the movable actuator frame tends to be displaced in position.